An area of contention in ELNES simulations using density functional theory (DFT) has been whether geometry optimisation is entirely necessary to obtain useful results. This issue is addressed for bulk magnesium oxide by comparison of results with and without energy minimisation of structures. An MgO (001) surface was investigated. Experiments were carried out to determine how the predicted oxygen K edges varied in different layers extending from the surface into bulk. Similarly the comparison of the MgO oxygen K edge in bulk and at the interface of Fe(001)/MgO(001) is of interest for spintronic devices. For this system, the oxygen K edge shows pre-edge intensity as compared to bulk MgO, which we attribute to additional states available due to transition metal d/ oxygen p orbital interactions at the interface.